The present invention relates to a drill pipe.
More particularly it relates to a drill pipe which has at least one tubular member provided with an external profiling and a central longitudinal passage throughout its length.
Drill pipes are known in many forms and for the most varied uses. They can be used for example as components of injection drilling anchors, which, as is known, correspond in structural terms to a drilling rod and after creation of the borehole remain in the borehole as a lost tool. In this case, after filling of the borehole with a cement suspension, the drilling rod is used in the manner of a rock anchor which, by means of an anchor head plate in combination with a tightening nut in the region of the mouth of the borehole, is tightened against the rock. For example, from DE-PS 936082, an injection drilling anchor is known at whose one end there is a drill head and at whose other end is fitted a removable threaded portion which serves for the screw fitting by means of the said tightening nut. The anchor rod is provided over its full length with helically wound beads as well as with transverse bores which are in permanent communication with a centrally extending longitudinal passage by means of which the rock debris created during the drilling process is carried away. After creation of the borehole, by means of the longitudinal passage as well as the transverse bores, a cement suspension is introduced into the borehole for the purpose of filling the borehole and anchoring the anchor rod. This suspension enters into any cracks and crevices in the rock and in particular, because of the bead-like configuration of the outside of the anchor rod, after hardening makes possible a secure positive anchorage between the anchor rod and the surrounding rock.
It is known, in the design of infection drilling anchors, to revert to structural components which are already known from drilling rods. For example, DE-PS 1483840 shows a rock drilling rod with a centrally arranged flushing passage which is provided in the region of a screwed-on drill head with outlet bores. The rock drilling rod or anchor red is extensible in use by means of a connecting sleeve which is provided with an internal thread into which is screwed a further anchor rod, with the inserted anchor rod additionally being equipped over its full length with a comparatively large thread in the manner of a circular thread. Such a rock drilling rod is basically; suitable for use as an injection drilling anchor, wherein the external thread of the anchor rod fulfils a transportation function during the drilling, in other words enabling the reverse flow of a flushing liquid which is charged with rock particles. In relation to the hardened cement the same thread fulfils an anchoring function, insofar as it produces the shape locking between anchor rod and surrounding borehole walls. Finally, the thread also fulfils a screw-fastening function, because it enables the screw fitting of a connecting sleeve, however with a drill head.
It is important for a trouble-free functioning of a rock anchor, particularly over the course of time, that it is arranged centrally within the borehole as far as is possible, so that a uniform cement overlay is provided around the anchor ever the full cemented length. A sufficient corrosion resistance is given only with an anchor which is reliably overlaid with cement. In practice, this requirement is often difficult to achieve, at without additional measures. If for example the anchor rod is arranged eccentrically because of spatial inhomogeneities along the wall of the borehole, then a uniform filling, especially overlaying or embedding of the drilling rod, cannot be guaranteed. An eccentric seating of the anchor rod within the cement body brings with it the danger that a part of the anchor rod will be subject to increased risk of corrosion, as a result of which in the course of time the main function of the rock anchor, namely the holding together of different rock strata, is brought into question.
From DE-PS 3828335 are known spacers used with injection drilling anchors, wherein these spacers consist of a retaining boss which directly surrounds the anchor rod and which is displaceable relative to the anchor rod. On this retaining boss are arranged three radially extending webs which are held together by an outer annular member. The use of this spacer means that during the creation of a borehole, and indeed before the introduction of an extension anchor rod, this spacer with its retaining boss is pushed over the end of the anchor rod which is already located in the borehole, wherein on the basis of a contact of the retaining boss against a coupling nut which makes possible the connection to an extension anchor rod, the spacer is introduced into the borehole together with the anchor rod during the further drilling extension. The position of the spacer is in this embodiment therefore established by the position of the coupling nut. During the drilling and after creation of the borehole there is in practice no or at least no simple possibility of examining the state of the spacer and the trouble-free functioning of the spacer. Thus, for example as a result of the high mechanical stresses during the drilling operation, and also due to local inhomegeneities of the bored rock, the spacer can be damaged, so that for these reasons under certain circumstances the centered effect no longer exists. Also, the spacer can prevent the leading away or extraction of rock particles by a flushing medium in many cases in dependence upon the local rock conditions as well as the properties of the rock particles which are freed as a result of the drilling process.
Finally, it is known in connection with the creation of so-called pre-drilled bores, to use spacers upon the setting in place of rock anchors, by means of which these are centered within the outer tube of the bore. It is known in these cases for the rock anchor to be introduced into a pipe filled with cement and to be held centered as far as possible within said pipe. The thus inserted spacer is of plastics material and is thus completely unsuitable in terms of its lack of strength for use with injection drilling anchors of the known type, in that they could scarcely withstand the high mechanical demands which are exerted during the drilling phase.